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<span class="token header-name keyword">User-Agent:</span> SOHUWapRebot
<span class="token header-name keyword">Accept-Language:</span> zh-cn,zh;q=0.5
<span class="token header-name keyword">Accept-Charset:</span> GBK,utf-8;q=0.7,*;q=0.7
<span class="token header-name keyword">Connection:</span> keep-alive
<span class="token header-name keyword">Content-Length:</span> 60408
<span class="token header-name keyword">Content-Type:</span>multipart/form-data; boundary=ZnGpDtePMx0KrHh_G0X99Yef9r8JZsRJSXC
<span class="token header-name keyword">Host:</span> w.sohu.com

--ZnGpDtePMx0KrHh_G0X99Yef9r8JZsRJSXC
<span class="token header-name keyword">Content-Disposition:</span> form-data; name=&quot;city&quot;

Santa colo
--ZnGpDtePMx0KrHh_G0X99Yef9r8JZsRJSXC
<span class="token header-name keyword">Content-Disposition:</span> form-data;name=&quot;desc&quot;
<span class="token header-name keyword">Content-Type:</span> text/plain; charset=UTF-8
<span class="token header-name keyword">Content-Transfer-Encoding:</span> 8bit
 
...
--ZnGpDtePMx0KrHh_G0X99Yef9r8JZsRJSXC
<span class="token header-name keyword">Content-Disposition:</span> form-data;name=&quot;pic&quot;; filename=&quot;photo.jpg&quot;
<span class="token header-name keyword">Content-Type:</span> application/octet-stream
<span class="token header-name keyword">Content-Transfer-Encoding:</span> binary
 
... binary data of the jpg ...
--ZnGpDtePMx0KrHh_G0X99Yef9r8JZsRJSXC--
</code></pre></div><p><code>boundary</code>表示分隔符，如果要上传多个表单项，就要使用<code>boundary</code>分割，每个表单项由<code>———XXX</code>开始，以<code>———XXX</code>结尾</p> <p>而<code>xxx</code>是即时生成的字符串，用以确保整个分隔符不会在文件或表单项的内容中出现</p> <p>每个表单项必须包含一个 <code>Content-Disposition</code> 头，其他的头信息则为可选项， 比如 <code>Content-Type</code></p> <p><code>Content-Disposition</code> 包含了 <code>type</code>和 一个名字为<code>name</code>的 <code>parameter</code>，<code>type</code> 是 <code>form-data</code>，<code>name</code>参数的值则为表单控件（也即 field）的名字，如果是文件，那么还有一个 <code>filename</code>参数，值就是文件名</p> <div class="language-kotlin extra-class"><pre class="language-kotlin"><code>Content<span class="token operator">-</span>Disposition<span class="token operator">:</span> form<span class="token operator">-</span><span class="token keyword">data</span><span class="token punctuation">;</span> name<span class="token operator">=</span><span class="token string">&quot;user&quot;</span><span class="token punctuation">;</span> filename<span class="token operator">=</span><span class="token string">&quot;logo.png&quot;</span>
</code></pre></div><p>至于使用<code>multipart/form-data</code>，是因为文件是以二进制的形式存在，其作用是专门用于传输大型二进制数据，效率高</p> <h3 id="二、如何实现"><a href="#二、如何实现" class="header-anchor">#</a> 二、如何实现</h3> <p>关于文件的上传的上传，我们可以分成两步骤：</p> <ul><li>文件的上传</li> <li>文件的解析</li></ul> <h3 id="文件上传"><a href="#文件上传" class="header-anchor">#</a> 文件上传</h3> <p>传统前端文件上传的表单结构如下：</p> <div class="language-html extra-class"><pre class="language-html"><code><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>form</span> <span class="token attr-name">action</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>http://localhost:8080/api/upload<span class="token punctuation">&quot;</span></span> <span class="token attr-name">method</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>post<span class="token punctuation">&quot;</span></span> <span class="token attr-name">enctype</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>multipart/form-data<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>input</span> <span class="token attr-name">type</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>file<span class="token punctuation">&quot;</span></span> <span class="token attr-name">name</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>file<span class="token punctuation">&quot;</span></span> <span class="token attr-name">id</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>file<span class="token punctuation">&quot;</span></span> <span class="token attr-name">value</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span><span class="token punctuation">&quot;</span></span> <span class="token attr-name">multiple</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>multiple<span class="token punctuation">&quot;</span></span> <span class="token punctuation">/&gt;</span></span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>input</span> <span class="token attr-name">type</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>submit<span class="token punctuation">&quot;</span></span> <span class="token attr-name">value</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>提交<span class="token punctuation">&quot;</span></span><span class="token punctuation">/&gt;</span></span>
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>form</span><span class="token punctuation">&gt;</span></span>
</code></pre></div><p><code>action</code> 就是我们的提交到的接口，<code>enctype=&quot;multipart/form-data&quot;</code> 就是指定上传文件格式，<code>input</code> 的 <code>name</code> 属性一定要等于<code>file</code></p> <h3 id="文件解析"><a href="#文件解析" class="header-anchor">#</a> 文件解析</h3> <p>在服务器中，这里采用<code>koa2</code>中间件的形式解析上传的文件数据，分别有下面两种形式：</p> <ul><li>koa-body</li> <li>koa-multer</li></ul> <h4 id="koa-body"><a href="#koa-body" class="header-anchor">#</a> koa-body</h4> <p>安装依赖</p> <div class="language-cmd extra-class"><pre class="language-text"><code>npm install koa-body
</code></pre></div><p>引入<code>koa-body</code>中间件</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">const</span> koaBody <span class="token operator">=</span> <span class="token function">require</span><span class="token punctuation">(</span><span class="token string">'koa-body'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
app<span class="token punctuation">.</span><span class="token function">use</span><span class="token punctuation">(</span><span class="token function">koaBody</span><span class="token punctuation">(</span><span class="token punctuation">{</span>
    multipart<span class="token operator">:</span> <span class="token boolean">true</span><span class="token punctuation">,</span>
    formidable<span class="token operator">:</span> <span class="token punctuation">{</span>
        maxFileSize<span class="token operator">:</span> <span class="token number">200</span><span class="token operator">*</span><span class="token number">1024</span><span class="token operator">*</span><span class="token number">1024</span>    <span class="token comment">// 设置上传文件大小最大限制，默认2M</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre></div><p>获取上传的文件</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">const</span> file <span class="token operator">=</span> ctx<span class="token punctuation">.</span>request<span class="token punctuation">.</span>files<span class="token punctuation">.</span>file<span class="token punctuation">;</span> <span class="token comment">// 获取上传文件</span>
</code></pre></div><p>获取文件数据后，可以通过<code>fs</code>模块将文件保存到指定目录</p> <div class="language-js extra-class"><pre class="language-js"><code>router<span class="token punctuation">.</span><span class="token function">post</span><span class="token punctuation">(</span><span class="token string">'/uploadfile'</span><span class="token punctuation">,</span> <span class="token keyword">async</span> <span class="token punctuation">(</span><span class="token parameter">ctx<span class="token punctuation">,</span> next</span><span class="token punctuation">)</span> <span class="token operator">=&gt;</span> <span class="token punctuation">{</span>
  <span class="token comment">// 上传单个文件</span>
  <span class="token keyword">const</span> file <span class="token operator">=</span> ctx<span class="token punctuation">.</span>request<span class="token punctuation">.</span>files<span class="token punctuation">.</span>file<span class="token punctuation">;</span> <span class="token comment">// 获取上传文件</span>
  <span class="token comment">// 创建可读流</span>
  <span class="token keyword">const</span> reader <span class="token operator">=</span> fs<span class="token punctuation">.</span><span class="token function">createReadStream</span><span class="token punctuation">(</span>file<span class="token punctuation">.</span>path<span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token keyword">let</span> filePath <span class="token operator">=</span> path<span class="token punctuation">.</span><span class="token function">join</span><span class="token punctuation">(</span>__dirname<span class="token punctuation">,</span> <span class="token string">'public/upload/'</span><span class="token punctuation">)</span> <span class="token operator">+</span> <span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">/</span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>file<span class="token punctuation">.</span>name<span class="token interpolation-punctuation punctuation">}</span></span><span class="token template-punctuation string">`</span></span><span class="token punctuation">;</span>
  <span class="token comment">// 创建可写流</span>
  <span class="token keyword">const</span> upStream <span class="token operator">=</span> fs<span class="token punctuation">.</span><span class="token function">createWriteStream</span><span class="token punctuation">(</span>filePath<span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token comment">// 可读流通过管道写入可写流</span>
  reader<span class="token punctuation">.</span><span class="token function">pipe</span><span class="token punctuation">(</span>upStream<span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token keyword">return</span> ctx<span class="token punctuation">.</span>body <span class="token operator">=</span> <span class="token string">&quot;上传成功！&quot;</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre></div><h4 id="koa-multer"><a href="#koa-multer" class="header-anchor">#</a> koa-multer</h4> <p>安装依赖：</p> <div class="language-cmd extra-class"><pre class="language-text"><code>npm install koa-multer
</code></pre></div><p>使用 <code>multer</code> 中间件实现文件上传</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">const</span> storage <span class="token operator">=</span> multer<span class="token punctuation">.</span><span class="token function">diskStorage</span><span class="token punctuation">(</span><span class="token punctuation">{</span>
  <span class="token function-variable function">destination</span><span class="token operator">:</span> <span class="token punctuation">(</span><span class="token parameter">req<span class="token punctuation">,</span> file<span class="token punctuation">,</span> cb</span><span class="token punctuation">)</span> <span class="token operator">=&gt;</span> <span class="token punctuation">{</span>
    <span class="token function">cb</span><span class="token punctuation">(</span><span class="token keyword">null</span><span class="token punctuation">,</span> <span class="token string">&quot;./upload/&quot;</span><span class="token punctuation">)</span>
  <span class="token punctuation">}</span><span class="token punctuation">,</span>
  <span class="token function-variable function">filename</span><span class="token operator">:</span> <span class="token punctuation">(</span><span class="token parameter">req<span class="token punctuation">,</span> file<span class="token punctuation">,</span> cb</span><span class="token punctuation">)</span> <span class="token operator">=&gt;</span> <span class="token punctuation">{</span>
    <span class="token function">cb</span><span class="token punctuation">(</span><span class="token keyword">null</span><span class="token punctuation">,</span> Date<span class="token punctuation">.</span><span class="token function">now</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">+</span> path<span class="token punctuation">.</span><span class="token function">extname</span><span class="token punctuation">(</span>file<span class="token punctuation">.</span>originalname<span class="token punctuation">)</span><span class="token punctuation">)</span>
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span>

<span class="token keyword">const</span> upload <span class="token operator">=</span> <span class="token function">multer</span><span class="token punctuation">(</span><span class="token punctuation">{</span>
  storage
<span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token keyword">const</span> fileRouter <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Router</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

fileRouter<span class="token punctuation">.</span><span class="token function">post</span><span class="token punctuation">(</span><span class="token string">&quot;/upload&quot;</span><span class="token punctuation">,</span> upload<span class="token punctuation">.</span><span class="token function">single</span><span class="token punctuation">(</span><span class="token string">'file'</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token punctuation">(</span><span class="token parameter">ctx<span class="token punctuation">,</span> next</span><span class="token punctuation">)</span> <span class="token operator">=&gt;</span> <span class="token punctuation">{</span>
  console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>ctx<span class="token punctuation">.</span>req<span class="token punctuation">.</span>file<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 获取文件</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span>

app<span class="token punctuation">.</span><span class="token function">use</span><span class="token punctuation">(</span>fileRouter<span class="token punctuation">.</span><span class="token function">routes</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre></div><h2 id="参考文献"><a href="#参考文献" class="header-anchor">#</a> 参考文献</h2> <ul><li>https://segmentfault.com/a/1190000037411957</li> <li>https://www.jianshu.com/p/29e38bcc8a1d</li></ul></div> <footer class="page-edit"><!----> <div class="last-updated"><span class="prefix">更新时间:</span> <span class="time">12/14/2021, 10:12:35 AM</span></div></footer> <div class="page-nav"><p class="inner"><span class="prev">
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